Marine Propulsion Devices, Systems and Methods

ABSTRACT

Some embodiments provide a propulsion system for a marine vessel that includes an electric motor-generator coupled between an internal combustion engine and a propeller through one or more clutches. The propulsion system includes a controller configured to adjust a torque load of the electric motor-generator based on factors such as rotational speed, propeller torque, and/or a peak torque output of the internal combustion engine. Some embodiments provide a propulsion assembly component including an electric motor-generator that can be installed in an existing marine propulsion system. Embodiments also provide methods for propelling a marine vessel.

CROSS-REFERENCES

This application claims the benefit of U.S. Provisional Application 61/389,248, entitled HYBRID PROPULSION DEVICES, SYSTEMS AND METHODS, filed Oct. 3, 2010, the content of which is hereby incorporated by reference in its entirety.

FIELD

Embodiments of the invention generally relate to propulsion and electric generation and storage systems for use in marine vessels and, more particularly to hybrid propulsion systems for marine vessels.

BACKGROUND

For many decades, internal combustion engines have been used to generate primary or auxiliary propulsive power and supply electricity for onboard loads across a broad range of marine vessels. In a typical installation, an internal combustion engine (ICE) is coupled to a propeller shaft through a transmission that provides for bidirectional propeller rotation in order to provide for ahead (foreword) and astern (reverse) propulsive motion of the vessel. In some cases electrical power is generated with the use of the ICE providing propulsive power and/or by an auxiliary ICE. For example, in smaller vessels, the engine may also be fitted with a generator that produces generates electricity for onboard electrical systems and for charging batteries used to supply the same onboard systems when the ICE is not running. A larger vessel may include one or more additional combustion engines fitted with generators to supply power for onboard loads.

A diesel engine usually operates at its highest efficiency when it is loaded to a point at or near its peak torque output (PTO) for any given rotational speed, as shown in FIG. 1. In marine settings, though, the torque required to turn a propeller usually only loads an ICE near its PTO when at or near full output, thus leading to losses in ICE efficiency at most speed settings. In some cases ICE efficiency can be improved by adjusting the pitch of a propeller's blades. However, an adjustable pitch propeller is mechanically complicated, requires additional maintenance and does not allow for an optimal blade shape at all pitch angles. A generator or alternator attached to the ICE for supplying electrical power and charging batteries can also increase the torque load on the ICE. Typical generators and alternators are often too small, though, to sufficiently load an ICE when the vessel is stationary and the ICE is only charging batteries. In addition, AC generators typically installed on larger vessels must run at a constant speed (e.g., 50 hz or 60 hz) to supply AC power at a desired frequency, thus limiting the amount and variability of the additional load that can be added to the ICE.

In some cases efficiencies can be gained through use of a diesel electric system, in which the ICE is decoupled from the propeller shaft and instead connected to an electric generator. The generator adds load to the ICE and the configuration allows the ICE's speed to be more easily regulated over a broader operating range, thus increasing ICE efficiency. The electricity generated is then used to power an electric motor connected to the propeller shaft. Efficiency gains are limited by losses in converting the ICE rotational energy to electricity and back to rotational energy driving the propeller shaft. An additional disadvantage with a diesel electric system is that it adds weight and takes up additional space in the vessel. Also, a failure of any single component (e.g., ICE, generator or electric propulsion motor) renders the system inoperable.

A serial hybrid system stores excess generator capacity in a high capacity battery bank, which can then be used later to propel the vessel or power onboard loads. However, a serial hybrid system also suffers from the losses inherent in converting mechanical energy to electricity and then converting the electricity back to mechanical energy for propulsion. In addition, this type of system adds even more weight and takes even more space when compared to a diesel electric system. Again, the failure of a single component in the system renders it inoperable.

In a parallel hybrid system, an ICE is coupled to a propeller shaft through a transmission that provides for ahead and astern propulsive motion of the vessel. An electric motor-generator is also coupled to the propeller shaft. The motor-generator can drive the vessel using stored energy from a high capacity battery bank and can also generate electricity when the vessel is underway or stopped. The generator adds load to the ICE and allows the ICE's speed to be more easily regulated over a broader operating range, thus increasing ICE efficiency. The operative connection between the ICE and the propeller shaft also avoids electro-mechanical conversion losses typical in other systems. A parallel hybrid system also only requires a single motor-generator rather than a propulsion motor and a separate generator, thus reducing the overall space and weight requirements in some cases. Even so, typical parallel hybrid systems still occupy more space than traditional non-hybrid engine installations. For example, the motor-generator is usually installed between the ICE and the transmission or between the transmission and the propeller, which in some configurations can require up to 6 to 8 additional inches in length over non-hybrid configurations. This can be an issue on any vessel, but is of particular concern in sailboats with auxiliary motors, where a desire for more usable space results in only very limited room for the auxiliary engine installation.

Some marine propulsion/energy systems also incorporate renewable energy sources to supplement power provided by an ICE. Common examples include solar panels and wind generators. On sailing vessels, a propeller can also turn a motor-generator when under sail. Typically, such renewable energy devices operate independently. For example, one device supplying power may raise the battery voltage to a point where another device's regulator partially or fully cuts the power being supplied by the other device. When this occurs, available power is lost, as it is not being put to work to power on-board systems and/or charge batteries.

SUMMARY

Some embodiments of the invention generally provide mechanical propulsive power for marine vessels and generate, store and/or use electric power to propel and/or supply onboard energy needs in marine vessels. According to an aspect of the invention, a propulsion system for a marine vessel is provided. The propulsion system includes an internal combustion engine and a first clutch which is operatively coupled to the internal combustion engine and an electric motor-generator which is also operatively coupled to the first clutch. An output shaft is operatively coupled to the electric motor-generator and to the internal combustion engine through the first clutch. The output shaft is configured to be operatively coupled to a propeller shaft. The propulsion system further includes a controller that is electrically coupled to the internal combustion engine and to the electric motor-generator, the controller is configured to adjust the torque load of the electric motor-generator based on the rotational speed of the internal combustion engine and the peak torque output of the internal combustion engine corresponding to the rotational speed.

According to another aspect of the invention, a method for propelling a marine vessel is provided. The method provides for using control circuitry to determine a desired torque output of an internal combustion engine that is operatively coupled to an electric motor-generator and a propeller; using the control circuitry to determine the current torque output; using the control circuitry to determine a torque output change by comparing the desired torque output to the current torque output; and using the control circuitry to adjust the torque load of the electric motor-generator based on the torque output change.

According to another aspect of the invention, a marine propulsion assembly is provided. The propulsion assembly includes a frame that has one or more supports configured to attach the frame to a marine vessel. A propeller shaft hub is rotatably coupled to the frame and includes an interior wall defining an opening adapted to receive a shaft operatively coupled to a propeller. The propeller shaft hub also includes a fastening mechanism to attach the propeller shaft hub to the shaft in a fixed rotational relationship. The marine propulsion assembly further includes a coupling flange attached to the propeller shaft hub. The coupling flange is configured to couple to an internal combustion engine. The marine propulsion assembly also includes a transmission that is rotatably coupled to the propeller shaft hub and an electric motor-generator rotatably coupled to the transmission.

According to another aspect of the invention, a propulsion system for a marine vessel includes a marine propulsion assembly having a propeller shaft hub that includes an interior wall defining an opening which is adapted to receive a shaft operatively coupled to a propeller. The assembly includes a frame with one or more supports configured to attach the frame to a marine vessel and the propeller shaft hub is rotatably coupled to the frame. The propeller shaft hub further includes a fastening mechanism to attach the propeller shaft hub to the shaft in a fixed rotational relationship. The marine propulsion assembly also includes an assembly coupling flange attached to the propeller shaft hub. The assembly coupling flange is configured to couple to an internal combustion engine. The marine propulsion assembly further includes a transmission that is rotatably coupled to the propeller shaft hub and an electric motor-generator rotatably coupled to the transmission. The transmission may include two or more pulleys and a belt that rotatably couple the electric motor-generator to the propeller shaft hub. The propulsion system for a marine vessel further includes an internal combustion engine including a system coupling flange coupled to the assembly coupling flange in a fixed rotational relationship. An output shaft is attached to the propeller shaft hub and to a propeller. The end of the output shaft is separated from the system coupling flange by a distance less than or equal to the fore-aft length of the assembly coupling flange.

Embodiments of the present invention can provide one or more of the following features and/or advantages.

In some cases, an embodiment may provide for more efficient power generation and usage for propulsion while a marine vessel is under power when compared with prior systems. In some cases, an embodiment may provide for more efficient generation of power for onboard systems while the vessel is underway. In some cases, an embodiment may facilitate more efficient charging of batteries for future propulsion usage and/or onboard electrical system usage while the vessel is not underway. In some cases, a system is configured to reduce reliance on an ICE by maximizing use of available renewable energy sources. In some cases a system is provided that integrates the control of propulsion, charge storage and onboard power needs into an automated control algorithm that maximizes use of renewable sources of power and minimizes fossil fuel usage and operator requirements. For example, in some cases a system may be provided that fully integrates the ICE, electric motor-generator, batteries and renewable charging sources and enables a single charging controller to combine the output from renewable and fossil fuel produced energy into one single charging current.

In some cases, a controller can monitor the output from renewable charging sources. By feeding each source into a separate DC-DC converter, each source can be combined into a single common charging source. In addition, each source can be controlled to achieve the greatest possible output under current conditions. For example, solar panels typically provide the maximum possible output when loaded to approximately 85% of their open circuit voltage. By periodically measuring the open circuit voltage, the panel can be loaded to its maximum power voltage. By loading each source to its maximum power point under current conditions and combining all sources into one charging current, the maximum output can be obtained. In some cases the controller is further configured to combine the charging current of the electric motor-generator with the charging current of at least one renewable energy source in order to charge the battery. The controller may be further configured to reduce the charging current of the electric motor-generator, as the charge level of the battery increases, before reducing the charging current of the renewable energy source(s).

When batteries are at a low state of charge, they can be charged with a high current. For example, a charger operating in a constant current mode is limited by the output of the charging source(s). Once the batteries achieve a certain state of charge, the terminal voltage will have risen to a point where it is desirable to switch to a constant voltage charge mode. This avoids possible damage if excessive voltage is applied. Once in this mode, the charge current required will fall as the batteries approach 100% of their state of charge.

In some cases, an embodiment may also extend the life of the ICE(s) contained in the vessel. Some embodiments provide the benefits of a hybrid propulsion system while also reducing or eliminating the weight penalty imposed by known hybrid systems.

In some cases the internal combustion engine may rotate the output shaft in only a first direction and the electric motor-generator can rotate the output shaft in the first direction and a second direction. For example, a traditional transmission of a hybrid propulsion system can be replaced by a light weight transmission designed to make the electric motor the primary propulsive source. One example includes a transmission that does not have a reversing gear and clutch mechanism. Removing the reversing gear can reduce the complexity and weight of the system. Instead, the electric motor-generator can provide reversing capability by virtue of its ability to rotate in either direction efficiently, with no need for gearing or clutches. Thus, the electric motor-generator becomes the primary source of propulsive power for short term maneuvering where quick changes in thrust magnitude and direction are often needed.

Accordingly, the ICE may not used for routine maneuvering and shorter distance usage. Instead, it may be dedicated to providing power for recharging batteries and for providing propulsive power only when the battery capacity is substantially depleted. By only running the ICE for periods when it has time to warm up and operate at its designed operational temperature and by providing adequate loading, the ICE's life is extended and its overall fuel efficiency is improved.

In some cases the electric motor-generator may be selectively coupled only to the output shaft, only to the ICE or to both. According to some embodiments, an electric motor-generator is always coupled to the propeller shaft. With the ICE's transmission in the neutral position, the electric motor-generator can provide propulsive power to the vessel. When the ICE is running and the transmission is engaged in forward or aft engagement, the electric motor-generator can absorb some of the available ICE rotational energy, thus supplying an electrical charging current to the batteries.

In some cases a controller is programmed to shut down the ICE anytime the boat is moving at, or below, a predetermined speed. The ICE is restarted and reengaged at, or above, a predetermined speed. This is useful in planing vessels, such as runabouts or sport fishermen. It can reduce fuel consumption and increase the life of the ICE by eliminating periods of idling in neutral or motoring at slow speeds, such as trolling. In addition, the electric motor-generator can provide extra torque to get the vessel up on plane and/or at top speed. Thus, a smaller ICE can be used, further reducing fuel consumption.

In some cases, the controller may be configured to adjust the torque load of the electric motor-generator in order to load the internal combustion engine with a torque that is within about 30% of the peak torque output corresponding to a particular rotational speed. In some cases, the controller may be configured to adjust the torque load of the electric motor-generator to load the internal combustion engine with a torque that is within about 10% of the peak torque output corresponding to a rotational speed. In some cases, the controller may be configured to adjust the torque load of the electric motor-generator to load the internal combustion engine with a torque that is substantially the same as the peak torque output corresponding to a rotational speed.

In some cases, the controller may be configured to adjust the torque load of the electric motor-generator based on a propeller torque load. As just one example, the propulsion system may include a propeller shaft operatively coupled to the output shaft and a propeller operatively coupled to the propeller shaft, so that the propeller torque load corresponds to the torque load of the propeller at the rotational speed. In some cases, the propeller may be a variable pitch propeller and the controller is further configured to adjust the pitch of the propeller's blades.

In some cases, a second clutch may be operatively coupled between the electric motor-generator and the output shaft to disengage the output shaft, the propeller shaft, and the propeller from the electric motor-generator and the internal combustion engine. The controller may be further configured to provide three operational configurations: a first configuration in which the first clutch is engaged and the second clutch is disengaged, to generate electricity with the internal combustion engine and the electrical motor-generator; a second configuration in which the first clutch is disengaged and the second clutch is engaged, for driving the propeller with only the electric motor-generator; and a third configuration in which the first clutch is engaged and the second clutch is engaged, for driving the propeller with the internal combustion engine and/or the electric motor-generator.

In some cases, the propulsion system may include at least one battery electrically coupled to the electric motor-generator, where the controller is further configured to operate the electric motor-generator with the battery; start the internal combustion engine to charge the battery when the battery reaches a first charge level; and stop the internal combustion engine when the battery reaches a second charge level. In some cases, the controller is further configured to start the internal combustion engine when the propulsion system is moving the marine vessel faster than a first speed and to stop the internal combustion engine when the vessel is moving slower than the first speed. In some cases, the controller is further configured to adjust the torque load of the electric motor-generator by adjusting a value of a charging current of the electric motor-generator.

In some cases a method of propelling a marine vessel includes adjusting a torque load based on a desired torque output that may be the peak torque output of the internal combustion engine for any given rotational speed. Determining a current torque output may include determining the torque load of the propeller. The propeller may also include a plurality of variable pitch blades, and determining the current torque output may further include adjusting the pitch of the variable pitch blades in order to adjust the torque load of the propeller.

In some cases, a method for propelling a marine vessel may include charging a battery with a charge current produced by the electric motor-generator. Charging the battery may also include charging the battery with a charge current produced by a renewable energy source and reducing the electric motor-generator charge current in order to maximize the charging with the renewable energy source charge current. In some cases, a method for propelling a marine vessel may include monitoring the charge level of a battery coupled to the electric motor-generator; running the internal combustion engine to charge the battery when the battery reaches a first charge level; and stopping the internal combustion engine when the battery reaches a second charge level. A method for propelling a marine vessel may include monitoring the speed of the marine vessel; running the internal combustion engine when the marine vessel is moving faster than a first speed; and stopping the internal combustion engine when the marine vessel is moving slower than the first speed. In some cases, a method for propelling a marine vessel may also include using the control circuitry to adjust the torque load of the electric motor-generator by adjusting a value of the charging current of the electric motor-generator.

In some cases, the transmission of a marine propulsion assembly may include two or more pulleys and a belt that rotatably couple the electric motor-generator to the propeller shaft hub. The transmission ratio may be selected to substantially match the electric motor-generator output speed to a desired speed for the shaft operatively coupled to a propeller. In some cases the fore-aft distance required by the coupling flange and the propeller shaft hub of a marine propulsion assembly is less than about four inches. In some cases, the coupling flange of the marine propulsion assembly is adapted to replace an existing propeller shaft coupling flange. In some cases, the assembly coupling flange of the propulsion system for a marine vessel may include a coaxial bore. The end of the output shaft is separated from the system coupling flange by a distance less than the fore-aft length of the assembly coupling flange.

In some embodiments, the controller is capable of reading a computer-readable medium that is used to store computer executable instructions. The controller may use the computer executable instructions when it is controlling the internal combustion engine, the battery, the electric motor-generator or a renewable source of electricity to optimize the efficiency of the internal combustion engine according to the embodiments, features or specifications disclosed herein. In some cases, the controller may include a computer-readable storage medium storing such executable instructions and/or information characterizing the peak torque output of the internal combustion engine for a plurality of rotational speeds.

In some cases a marine propulsion assembly includes a frame and coupling configuration that allows it to be installed in a compact space with a minimum of additional weight. In some cases, a marine propulsion assembly is configured to be retrofitted into an existing engine bed, such as on a sailing vessel.

An advantage of retaining an ICE in a hybrid propulsion system is the higher energy density of fossil fuels compared to the energy density of current battery technology. This gives the ICE a decided advantage for powering a marine vessel over longer distances. In other situations, the operational properties of an electric motor provide advantages over an ICE. These properties include quiet operation, ability to rotate in both clockwise and counterclockwise direction efficiently, the ability to rotate at much lower speeds, the ability to generate high torque from virtually zero speed to full rated speed, no need to operate at a minimum idle speed in order to remain operational (a minimum idle speed wastes fuel), and the instant availability of power with no starting and warm up period. A low rotating mass combined with full torque at all speeds, also results in rapid acceleration. In addition, an electric motor has the ability to produce torque far in excess of its continuous torque rating for short periods of time.

These and other characteristics give an electric motor advantages for maneuvering and other forms of short distance operation. For example, these characteristics can be useful when entering and leaving a dock or pier and when anchoring or maneuvering in tight quarters, such as entering a marina slip. The slow speed capability is also useful in certain situations such as fishing (e.g., trolling). The quiet operation makes for easier communication both for normal conversation and when coordinated crew activities are needed, such as when docking or anchoring.

These and various other features and advantages will be apparent from a reading of the detailed description. The above summary of various embodiments, features, and/or advantages is not intended to describe each illustrated embodiment or every implementation of the invention. Rather, the illustrated embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements.

FIG. 1 is a graph relating torque output and rotational speed of an internal combustion engine used in a marine propulsion system.

FIG. 2 is a block diagram of a marine propulsion system according to some embodiments of the invention.

FIG. 3 is a block diagram of a marine propulsion system including a control system in accordance with an embodiment of the invention.

FIG. 4 is a block diagram of a battery charging scheme for a marine propulsion system in accordance with an embodiment of the invention.

FIG. 5 is a flow diagram illustrating a method for adjusting the torque load within a marine propulsion system in accordance with an embodiment of the invention.

FIGS. 6A and 6B are perspective and side views, respectively, of a marine propulsion system in accordance with an embodiment of the invention.

FIGS. 7A-7C are side and perspective views of a marine propulsion assembly in accordance with an embodiment of the invention.

FIGS. 8A-8D are various views of an electric motor-generator coupling assembly in accordance with an embodiment of the invention.

FIGS. 9A-9E are side and perspective views, and an exploded assembly view of a shaft hub, coupling flange, and transmission pulley of the electric motor-generator coupling assembly of FIGS. 8A-8D.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides some practical illustrations for implementing exemplary embodiments of the present invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements, and all other elements employ that which is known to those of ordinary skill in the field of the invention. Those skilled in the art will recognize that many of the noted examples have a variety of suitable alternatives.

Throughout the specification, any references to such relative terms as top, bottom, fore, aft and the like, are intended for convenience of description and are not intended to limit the present invention or its components to any one positional or spatial orientation. It will be further understood that various dimensions of the components in the figures may vary depending upon specific applications and intended use of the invention without departing from the scope of the invention.

FIG. 2 is a block diagram of a marine propulsion system 100 according to some embodiments of the invention. The propulsion system 100 generally includes an internal combustion engine (ICE) 102 operatively coupled with an electric motor-generator 106 to drive a propeller 112, and thus can in some cases be referred to as a hybrid propulsion system. A typical small marine diesel engine can be a Yanmar 3YM20 or a Volvo D1-30. The ICE 102 is operatively coupled to the electric motor-generator 106 through a first clutch 104A and a common shaft 107. For example, first clutch 104A can selectively and rotatably couple a drive shaft or fly wheel of ICE 102 to the common shaft 107. The electric motor-generator 106 is operatively coupled to the common shaft 107 without a clutch. In some cases it may be coupled by gears, belts or directly, as in the case where the common shaft 107 passes through the motor-generator's rotor.

The electric motor-generator 106 is operatively coupled to an output shaft 108 through the common shaft 107 and a second clutch 104B. Output shaft 108 transfers the propulsive power of the drive system (including the ICE 102 and the electric motor-generator 106) to the propeller 112 either directly or indirectly, depending upon the configuration of the particular marine vessel in which the system 100 is installed. In some cases the output shaft 108 is configured to be coupled to a separate propeller shaft 110, which is the drive shaft directly connected with the propeller 112. The coupling between the output shaft 108 and the propeller shaft 110 can be a direct attachment or an indirect coupling, e.g., through an inboard transmission having gears, belts, pulleys and the like. This allows for matching the output shaft speed range to any desired propeller shaft speed range. In a simple example, the output shaft 108 may be the same as the propeller shaft 110 and be directly connected to the propeller 112.

Through discrete use of clutches 104A and 104B, the electric motor-generator 106 can be selectively coupled to only the output shaft 108, to only the ICE 102 or to both the output shaft 108 and to the ICE 102 at the same time. Accordingly, the propulsion system 100 can provide at least three operational configurations. In a first configuration, the first clutch 104A is engaged and the second clutch 104B is disengaged, thus coupling the ICE 102 to the electric motor-generator 106 to generate electricity to provide system power and charge a battery 116. In a second configuration, the first clutch 104A is disengaged and the second clutch 104B is engaged, thus allowing the electric motor-generator 106 to drive the propeller 112 independently of the ICE 102. In some cases this configuration also enables extracting power from the rotating propeller, such as when a vessel is under sail. In a third configuration, the first clutch 104A is engaged and the second clutch 104B is engaged. This configuration enables the ICE 102 and/or the electric motor-generator 106 to drive the propeller 112.

While FIG. 2 illustrates the use of the first and second clutches 104A, 104B, in some cases one or both of these clutches are optional and may not be used. For example, in some cases the electric motor-generator 106 may be directly coupled to the ICE 102 in a fixed rotational relationship without a clutch. In some cases the electric motor-generator 106 may be directly coupled to the propeller 112 without a clutch. In addition, the first and second clutches 104A, 104B can take any suitable form and those skilled in the art will appreciate that a number of designs are possible. In some cases a “dog” clutch is provided as will be described further herein.

Marine propulsion systems typically include a transmission that includes at least a clutch that enables an operator to disengage an ICE from the propulsion system and a reversing gear that enables an ICE to drive the vessel in multiple directions. Referring to the embodiment in FIG. 2, in some cases the propulsion system 100 optionally does not include a traditional transmission that would normally enable the ICE to propel a vessel both ahead and astern. For example, the system 100 may include a “lightweight” transmission that simply provides one or more speeds in a single direction. In such a case, the output shaft 108 is rotatable by the ICE 102 in only a first direction. However, the output shaft 108 is rotatable by the electric motor-generator 106 in both the first direction and an opposite second direction (e.g., clockwise and counterclockwise). Accordingly, the propulsion system 100 can use the electric motor-generator 106 to provide reversing capability by virtue of its ability to rotate in either direction efficiently, with no need for gearing or clutches. Thus, the electric motor can be the primary source of propulsive power for short term maneuvering where quick changes in thrust magnitude and direction are often needed. The omission of an additional clutch and reversing gear can thus reduce the complexity, cost and weight of the propulsion system 100.

In some cases the propeller 112 may optionally be a variable pitch propeller to provide additional functionality and benefits. For example, a variable pitch propeller can be used to provide aft thrust by reversing the propeller blades. This could allow the ICE 102 to generate aft thrust without the use of a bi-directional transmission. In addition, the blade pitch can be adjusted to provide additional torque which may be needed in certain situation, such as, for example, driving into very strong wind and wave conditions. In the case of a sailboat, the blade pitch can be adjusted to either provide for the most efficient battery charging while under sail, or adjusted to minimize drag, and thus improve sailing efficiency.

Different coupling configurations between the ICE 102, the motor-generator 106, and the propeller 112 provide distinct functional characteristics. For example, when the electric motor-generator is coupled only to the output shaft 108 and propeller 112, the electric motor-generator 106 is the only source of propulsive power. It can rapidly drive from full power ahead to full power astern with no shifting. In addition, it can charge the battery 116 and provide system power in a sailboat when under sail by extracting power from the rotating propeller.

In a coupling configuration where the electric motor-generator 106 is only coupled to the ICE 102, the electric motor-generator 106 can be used to start the ICE 102. The electric motor-generator 106 can also function as a generator charging the battery 116. This coupling configuration allows for battery charging while the vessel is not in motion and without access to shore power, such as when riding at anchor.

In a coupling configuration where the electric motor-generator 106 is coupled to both the ICE 102, and to the propeller shaft 110, the electric motor-generator 106 can be used to start the ICE 102 and the electric motor-generator 106 can also function as a generator for charging the battery 116 while the vessel is underway by means of the ICE 102. As will be discussed in more detail, in this coupling configuration the electric motor-generator 106 can be used to add an advantageous amount of load to the ICE 102, such that the propulsive load and the generating load combine to optimally load the ICE 102. Improving the load on the ICE 102 can minimize overall fuel consumption and extend the internal combustion engine's 102 service life. When the vessel is stopped, and charging is not desired, the ICE 102 can be turned off. The ICE 102 can then optionally serve as a brake to stop propeller rotation which minimizes wear on the shaft seal and support bearing.

Through careful design, embodiments including propulsion system 100 can be constructed so as to occupy substantially the same space, and to weigh substantially the same, as a traditional marine propulsion system including an ICE and transmission. In addition, increased efficiency will permit a reduced fuel load while maintaining substantially the same range and electrical power generating capability. The reduction in fuel load can substantially offset the battery weight for electrical power storage. Further, in typical traditional installations, an ICE is sized for use in extreme conditions, such as avoiding another vessel or navigating against a strong current in a narrow channel. By sizing the ICE 102 to deliver only full power needed under normal usage, a smaller and lighter engine may optionally be used. In such a case, the electric motor-generator 106 can provide the additional torque needed for extreme situations. The result may be a substantial overall weight reduction.

Referring again to FIG. 1, an ICE produces power more efficiently when it can be loaded more closely to its PTO. In addition, peak efficiency occurs only over part of the ICE rotational speed range. Therefore, maximum efficiency can be obtained by substantially loading the ICE to a point at or near its PTO and operating within its most efficient rotational speed range. Some embodiments provide a control system that can vary the torque load on the ICE based on information such as a design torque vs. rotational speed curve for a specific ICE, propeller torque load under current conditions, ICE rotational speed, available torque from the electric motor-generator, battery state of charge, electrical power load, and other types of information.

FIG. 3 is a block diagram of a marine propulsion system 200 including a control system 202 in accordance with an embodiment of the invention. The propulsion system 200 incorporates the embodiment shown in and described with respect to FIG. 2, including the electric motor-generator 104 coupled between the ICE 102 and the propeller 112 through first and second clutches 104A, 104B. The propulsion system 200 includes one or more batteries 116 electrically connected to the electric motor-generator 106, and a controller 118 electrically connected to the system 200. The controller 118 generally directs the operation of one or more components within the propulsion system 200, and may optionally provide or communicate through a user interface 205 to allow a human operator to configure and/or control the propulsion system 200. For example, the user interface 205 can be wholly or partially computer-generated and/or may include physical control switches, levers, buttons, and other indicators, including, for example, a throttle quadrant and/or a mode selector.

The controller 118 can be provided by hardware, software, or a combination of hardware and software. As shown in FIG. 3, the controller 118 is illustrated having processing circuitry 206 and memory 208 that stores instructions for execution by the processing circuitry 206. The processing circuitry 206 can be any suitable computer processor (e.g., a microprocessor, microcontroller, central processing unit, etc.). The memory 208 can be any suitable physical, non-transitory (i.e., not a signal per se) memory component, such as volatile or non-volatile memory, including various types of RAM and/or ROM, disk, tape, CD, and/or DVD storage. The controller 118 may also or alternatively be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. Controller 118 may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

The control system 202 includes several control and information lines connecting the controller 118 to various components within the propulsion system 200. For example, the controller 118 is in communication with the ICE 102 and receives information from the ICE such as engine speed and fuel consumption. The controller also sends a speed control signal to the ICE 102 to control the rotational speed of the ICE. The controller 118 is also in communication with the electric motor-generator 104, receiving information such as the speed and current of the motor-generator and optionally providing control signals to the motor-generator 104. The controller may optionally be electrically coupled to a number of other components within the propulsion and/or control systems. For example, the propulsion and/or control systems may include one or more sources 210 of renewable energy, such as a wind turbine or solar panel. The propulsion and/or control systems may in some cases include one or more sensors for gathering and communicating information about system components to the controller 118. One example includes a torque sensor 212 that senses the torque load of the electric motor-generator 104 and/or the torque load of the propeller 112. Another example is a communication line between the controller 118 and one or more rechargeable batteries 116, which can allow the controller to monitor the battery voltage and power levels. In addition, although not shown, the controller 118 may optionally be coupled to the first and/or the second clutch 104A, 104B to provide automatic clutching between the electric motor-generator, the ICE, and/or the propeller.

The controller 118 is preferably (though not necessarily) configured to vary the torque load presented by the electric motor-generator 106 to the ICE 102. For example, the controller 118 may increase or decrease the torque generated by the electric motor-generator 106 in order to load the ICE 102 to a point near or at the ICE's peak torque output (PTO) for a given rotational speed. In some cases the controller 118 has access to information (e.g., stored on memory 208) characterizing the peak torque output of ICE 102 for a plurality of rotational speeds. The controller 118 can then determine a desired torque output or load (e.g., at or near PTO) for a particular rotational speed using the ICE's torque information. In some cases the desired torque output may be substantially the same as the PTO of the ICE. However, several other ranges of torque output near to, but below PTO may also be satisfactory. For example, in some cases the desired torque output may be within about 30% of the PTO. In some cases the desired torque output may be within about 10% of the PTO.

By determining the current torque output, the controller can determine a change in torque output that should be made to adjust the torque load on the ICE nearer to the desired torque output. In some cases the controller 118 can adjust the torque load on the ICE by modifying the charging current of the electric motor-generator. Since motor-generator torque load is proportional to charging current, the charging torque can be adjusted by using the controller 118 to change the electric motor-generator's charging current according to the calculated change.

In some cases the controller 118 can optionally be configured to determine the torque adjustment based on the current propeller torque load. For example, in some cases an automatic control algorithm (e.g., a proportional-integral-derivative (PID) control algorithm) can determine the desired torque adjustment for a given speed using the following relationship:

PTO−propeller torque load=torque available for charging.

In some cases, the controller 118 is programmed to only run the ICE 102 when it can be loaded near to or substantially PTO and to shut it down when conditions are otherwise. This operating scheme can provide efficient propulsion and electrical generation for storing in batteries. For example, in some cases the controller 118 is programmed to shut down the ICE 102 anytime the vessel is moving at, or below, a predetermined speed. The ICE 102 is restarted and reengaged at, or above, a predetermined speed. This is useful in planing vessels, such as runabouts or sport fishermen. It can reduce fuel consumption and increase the life of the ICE by eliminating periods of idling in neutral or motoring at slow speeds, such as trolling. In addition, the electric motor-generator 106 can provide extra torque to get the vessel up on plane and/or at top speed. Thus, a smaller ICE can be used, further reducing fuel consumption.

In some cases, the one or more batteries 116 are of the type that can be charged and discharged efficiently (e.g., TPPL or LiFePO4 chemistries) so that the vessel can be operated over long distances in a mode where the ICE 102 runs long enough to recharge the batteries 116. After charging batteries 116 with the ICE 102, the controller 118 shuts down the ICE 102 and the electric motor-generator 106 runs until the batteries 116 are depleted to a predetermined level. At this point, the ICE 102 can be started again and run in a optimally loaded state until the batteries 116 are recharged. The controller 118 can repeat this cycle for as long as necessary. According to this example, this mode reduces the likelihood that the ICE 102 will be operated for short periods and is preferably optimally loaded when it does run. Accordingly, this control mode can provide for increased fuel economy and extended ICE life.

FIG. 4 is a block diagram of a battery charging scheme 300 for a marine propulsion system in accordance with an embodiment of the invention. As just one example, the propulsion system 200 illustrated in FIG. 3 can carry out the charging scheme 300. In this example, the controller 118 acts as a single charging controller that integrates the ICE 102, electric motor-generator 104, batteries 116 and renewable charging sources such as renewable sources 204 and the propeller's regenerative power. The controller 118 thus combines the output from multiple renewable and fossil fuel energy sources into one single charging current that is delivered to the batteries 116.

In traditional piece meal systems, one charging source can and often does raise the battery voltage to a point where the regulators in the other devices think the battery is fully charged and stop contributing charge current, even though they could. For example, the regulated output voltage from the ICE's generator might be high enough to exceed the full charge voltage setting of a wind generator. In some circumstances, the wind generator may stop providing any charge current. Under this condition, more fossil fuel than necessary will be burned because the available energy from the wind generator is not utilized. A similar condition can and does occur when combining the outputs of multiple renewable sources. For example, when solar panels are connected in parallel, the one with even a very slightly lower charging voltage will not contribute current. By employing a controller that monitors each separately and combines their output into one common charging current, this limitation can be avoided and each source can contribute to the fullest extent possible at any given time.

Returning to FIG. 3, it should be appreciated that the controller 118 can provide one, two, a few, or many control modes for operating the propulsion system 200 depending upon the desired complexity and number of features for a particular implementation. FIG. 5 is a flow diagram illustrating one method 400 for adjusting the torque load within a marine propulsion system in accordance with an embodiment of the invention. The method 400 includes determining 302 (e.g., with the controller 118) a desired torque output of the ICE 102 and determining 304 a current torque output of the system. The method 400 (e.g., implemented by the controller 118) then determines 306 a desired change in torque output by comparing the desired torque output to the current torque output. After determining the desired change, the torque load of the electric motor-generator 106 is adjusted 308 based on the torque output change.

In some cases the controller 118 may optionally implement the method 400 as part of a control mode corresponding to underway propulsion and charging. As noted above, an ICE produces power most efficiently when loaded at a point near or at its PTO. Additionally, peak efficiency occurs only over part of its rotational speed range. Therefore, maximum efficiency can be obtained by loading the ICE 102 to a point at or near its PTO and operating within its most efficient rotational speed range. The controller 118 can accomplish this by basing operation on several pieces of sensed and/or received information, such as, for example, design torque vs. rotational speed curve for the specific ICE, propeller torque load under current conditions and current rotational speed, battery state of charge (SOC) and/or current electrical power load. In some cases all but the propeller torque load are readily acquired using low cost sensing means. The propeller torque can optionally be measured directly through the use of torque sensors or inferred through knowledge of the system and measurement of other available data.

As shown in FIG. 3, a torque sensor 212 can be employed such that propeller 112 torque is directly measured in real time. Torque applied to the motor-generator 106 can also be measured directly through the use of properly placed torque sensors. By making the ICE's torque versus rotation speed curve available to the controller 118, the proper charging torque load can be easily calculated by subtracting measured propeller load from PTO, as shown in the relationship above. Since motor-generator torque load is proportional to charging current, the charging torque is adjusted by adjusting the charging current to the calculated difference.

In some cases the propeller torque data can be inferred rather than measured. In one case, a calibration can occur. Since motor torque is proportional to motor current, propeller torque load can be inferred by driving the propeller 112 with the electric motor-generator 106. By doing this at various speeds, and recording the data (e.g., in memory 208), a table of values can be generated that provides the propeller torque load at multiple speeds. In addition, points between the measured points can be derived by extracting a mathematical formula that fits the data or by some means of interpolation between points. In some cases a more accurate measurement can by acquired by measuring vessel speed in conjunction with motor current and rotational speed. If done in varying sea conditions, such as calm flat water, motoring into wind and seas and motoring with wind and wave conditions, a model with greater accuracy in varying conditions can be generated. In some cases, the torque load can be inferred from the engine manufacturer's specifications and from the boat and/or propeller manufacturer's specifications.

Accordingly, one or more of these control methods can be used to load the ICE 102 such that it will operate more efficiently at any given shaft rotational speed when the batteries 116 can accept the full rate of charge required. Of course other methods can be employed in measuring or estimating the propeller torque load. As an excessive torque load can lead to damage to the ICE 102, it can be helpful to apply an appropriate safety margin to the charging torque load command. This margin should be based on an analysis of the accuracy of the method employed.

In some cases the controller 118 may optionally implement another control mode corresponding to charging the batteries 116 when not underway. In this control mode, the controller 118 is free to set the rotational speed of the ICE 102 because the second clutch 104B can be disengaged. When the batteries 116 are at a low charge state, the ICE 102 is commanded to run at the upper end of the highest efficiency part of its operating envelope.

In a representative example including a Kubota Z602-E3B engine, this range is from 1800 RPM to 2800 RPM. As such, the controller 118 initially loads the ICE 102 to a point at or near the PTO level corresponding to 2800 RPM. This will produce the maximum power at the minimum fuel consumption/watt produced, resulting in a minimum charging time period consistent with minimizing fuel consumption. As the battery charge state rises to a point where it will not accept charge at this rate, the controller 118 can reduce the rotational speed of the ICE, while also adjusting the torque load to remain at or near the PTO corresponding to the new rotational speed (e.g., with the method 400). Thus, highly efficient charging is maintained over a large segment of the battery charging profile.

In some cases the controller 118 may optionally implement other control modes. For example, once the ICE 102, electric motor-generator, and battery 116 are operating out of the charging range where PTO can be maintained, a number of strategies can be used to maximize use of renewable energy sources and minimize ICE fuel usage. In some cases, the ICE can be shut down and the vessel can continue underway by drawing power from the batteries for propulsion via the electric motor-generator 106 and for onboard (house) needs. This can continue until the batteries 116 are discharged to a predetermined point. At this point, the ICE 102 can be restarted to begin the cycle over again.

In some cases, the controller 118 can monitor the output from multiple renewable charging sources and feed each source into a separate DC-DC converter so as to combine each source into one common charging source. Accordingly, each source can be independently controlled to achieve the greatest possible output under current conditions. For example, solar panels typically provide the maximum possible output when loaded to approximately 85% of their open circuit voltage. By periodically measuring the open circuit voltage, the panel can be loaded to its maximum power point voltage. By loading each source to its maximum power point under current conditions and combining all sources into one charging current, an increased output can be obtained.

In some cases the batteries 116 can be charged with a high current when the batteries 116 are at a low state of charge. For example, in some cases the charger will be operating in a constant current mode limited by the output of the charging source(s). Once the batteries 116 achieve a certain state of charge, the terminal voltage will have risen to a point where it is desirable to switch to a constant voltage charge mode. Switching can help avoid damage possible if excessive voltage is applied. Once in this mode, the charge current required will fall as the batteries approach 100% charged. Once the current has fallen to a point where the renewable sources can supply the required current, the ICE 102 can be shut down. In some cases the renewable sources are preferably kept at full current output until the ICE's current is not needed. To gain greater efficiency, the ICE 102 can in some cases be shut down as soon as its loading is reduced below PTO at a predetermined minimum rotational speed. The predetermined speed can be based on an efficiency determination.

For any particular control mode, the controller 118 can be configured via hardware or software programming to interact with and control the operation of the system components to provide the particular mode. Further, in some cases a switch or other mechanism (e.g., provided as part of interface 205) can allow manual selection of one or more provided control modes. In some cases, the switching mechanism can allow for selecting one of three operating modes: an automatic algorithm, a manual override, or an “off” mode, which prevents the ICE from running. Renewable charging sources can remain active in the off mode, or can also be disabled.

Examples of other control modes that can be provided by the controller 118 include, but are not limited to following:

A starting sequence for starting the ICE 102 when not underway.

A starting sequence for starting the ICE 102 when underway.

A control sequence that decouples the ICE 102 from the electric motor-generator 106 anytime reverse or aft thrust is needed.

A control sequence that regenerates power by extracting power from the turning propeller 112 (e.g., in a sailboat while sailing). The propeller 112 of a vessel moored or anchored can also be turned by a significant current or tidal flow.

A controller 118 that works to extract the maximum power available from renewable resources, such as wind and solar.

A controller 118 that selectively reduces power derived from shore power or the ICE 102 in favor of renewable sources when more than enough total power is available to meet battery charging and load needs.

A control algorithm that optimizes fuel efficiency of the ICE 102 when underway by adjusting the charging current provided by the motor-generator 106 to load the ICE 102 to its optimal efficiency point for any given engine rotational speed.

A control algorithm that optimizes torque loading and engine speed of ICE 102 to achieve maximum fuel efficiency when not underway and when charging batteries 116.

An automatic propulsion and charging algorithm that works to optimally start, run and stop ICE 102 to achieve maximum fuel efficiency when underway.

An automatic charging algorithm that works to optimally start, run and stop ICE 102 to achieve maximum fuel efficiency when not underway.

An automatic charging algorithm that selectively decreases charging current from shore power or ICE 102 before reducing charging current from renewable sources when more charging current is available than can be absorbed by batteries 116.

A manual override mode for an automatic propulsion and charging algorithm to allow an operator to start and run the ICE 102 when the automatic sequence may not call for starting the ICE 102. This can be useful when the operator anticipates a significant time underway and wants to make sure that the batteries 116 are fully charged on arrival. It is also useful when the operator wants to start a battery charging sequence at a convenient time, so that it does not run later when sleeping or entertaining, for example.

A control algorithm that allows the electric motor-generator to provide additional propulsive power for extreme conditions, such as collision avoidance or navigating against a strong current, thus allowing for a lighter overall system.

A control algorithm that automatically stops the ICE when at, or below, a predetermined speed and restarts the ICE when at, or above, a predetermined speed.

A control algorithm that can assist an ICE in accelerating a vessel to a planing speed and can add torque to allow for a higher top speed, thus reducing the size and weight of the ICE.

FIGS. 6A and 6B are perspective and side views, respectively, of a marine propulsion system 500 in accordance with an embodiment of the invention. The propulsion system 500 is similar in many respects to the propulsion system 200 shown in FIG. 3. In this embodiment, the ICE 502 includes a standard ICE transmission 504, which in some cases optionally includes a reversing gear and clutch. The propulsion system 500 also includes a marine propulsion assembly 600 that provides an electric motor-generator 601 and operatively couples the motor-generator 506 to the propulsion system 500. In certain cases the marine propulsion assembly 600 can be considered a “retrofit” propulsion assembly because it is configured to couple into an existing standard marine propulsion system (e.g., in which an ICE is the only source of propulsion) already onboard a vessel.

The propulsion assembly 600 generally includes a frame 602 and may optionally include support arms 604 configured to attach to the existing ICE 502 drive system. As will be discussed further herein, the propulsion assembly 600 includes a propeller shaft hub 606 rotationally attached and fixed to an assembly coupling flange 608. The term “propeller shaft hub” is used to indicate that the shaft hub 606 is configured to receive and couple to a propeller shaft and/or another shaft that couples to the propeller shaft and propeller. For example, upon installing the retrofit assembly 600 within an existing propulsion system, the propeller shaft hub 606 in some cases is configured to receive and couple to an existing shaft coupled between the system ICE and propeller. The existing shaft may simply be the propeller shaft that is directly connected to the propeller, or it could be an output shaft 610 shown in FIGS. 6A and 6B that is coupled to the propeller shaft through a further transmission.

As shown in FIGS. 6A and 6B, the assembly coupling flange 608 is configured to mate with and couple to a coupling flange 510 of the ICE drive train. In this case the drive coupling flange 510 is coupled to the ICE 502 through the ICE transmission 504, though in some cases the drive coupling flange 510 may be directly attached to another portion of the ICE 502 (e.g., in the absence of transmission 504). As used herein, the term “drive coupling flange” refers to a coupling flange of the existing ICE drive system, which is normally coupled to the existing propeller shaft coupling flange before installation of the retrofit assembly 600.

As will be discussed further herein, the propeller shaft hub 606 and optionally the assembly coupling flange 608 are hollow. The interior opening in the shaft hub 606 (and optionally the assembly coupling flange 608) allows the shaft hub 606 (and optionally the coupling flange 608) to receive the existing propeller/output shaft 610 while requiring little to no coaxial space between the end of the propeller/output shaft 610 and the existing ICE drive system and drive coupling flange 510. Accordingly, the retrofit assembly 600 can be installed in a number of existing marine propulsion systems mounted in a wide variety of engine bays, and a large amount of additional coaxial space is not required for the retrofit assembly 600. This can be especially helpful for small auxiliary engine bays, such as on sailing vessels.

FIGS. 7A-7C are side and perspective views of a version of the marine propulsion assembly 600 in accordance with an embodiment of the invention. As mentioned with respect to FIGS. 6A-6B, the propulsion assembly 600 includes a frame 602 to which the electric motor-generator 601 is mounted. The propeller shaft hub 606 is rotationally fixed to the assembly coupling flange 608, and the frame 602 is rotationally coupled with the propeller shaft hub 606 with the assistance of a bearing (not shown). As will be discussed further herein, an assembly transmission operatively couples the electric motor-generator 601 and the propeller shaft hub 606 and the assembly coupling flange 608. The propulsion assembly 600 also includes optional support arms 604 and support flanges 612 for fixing the propulsion assembly to the ICE drive system and/or within the existing engine bay. In this case the propulsion assembly 600 includes an optional splash guard 614 mounted over the electric motor-generator 601 and a cover 616 mounted over the controller 618. It should be noted that in FIGS. 7A-7C the cover 616 is illustrated as semi-transparent to reveal the controller 618 beneath, though in practice the cover can be formed from a material having any degree of transparency or no transparency.

In addition, although not shown, control and data wires are provided to electrically connect the controller 618 with the other components of the propulsion system, such as is described with reference to the system 200 shown in FIG. 3.

As shown in FIGS. 6A-6B and 7A-7C, the propulsion assembly 600 is configured to directly couple to the drive coupling flange 510 through the assembly coupling flange 608 (e.g., via bolts). In the example illustrated in FIGS. 7A-7C, the propulsion assembly 600 also includes a clutch 620 with a first side 622 rotationally fixed to the propeller shaft hub 606 and a second side 624 configured to be rotationally fixed to the propeller/output shaft. Although not shown, a sliding mechanism is coupled to the second side 624 of the clutch in order to move the second side 624 into and out of engagement with the first side 622. In this case the clutch comprises an optional dog clutch that operates by interference, although it should be appreciated that any suitable clutch design can be used.

Accordingly, the clutch 620 enables the propeller/output shaft to be selectively engaged or disengaged from the propulsion assembly 600 and ultimately from the ICE 502. While the illustrated example shows the clutch 620 positioned opposite the frame 602 from the assembly coupling flange 608 (and also the ICE), it should be appreciated that the position of the clutch 620 can be changed to the other side of the frame. In addition, two clutches 620 (one between the propeller/output shaft and the propulsion assembly 600 and one between the propulsion assembly 600 and the ICE 502) can optionally be used if another degree of disengagement is desired.

FIGS. 8A-8D show various views of an electric motor-generator coupling assembly 700, in accordance with an embodiment of the invention, that is a variation of the frame and coupling assembly illustrated in FIGS. 6A-7C. The coupling assembly 700 generally includes a frame 702, support arms 704, and support flanges 712 as shown in the example of FIGS. 7A-7C. The support arms 704 and support flanges 712 are configured to attach frame 702 to the existing ICE and/or the vessel engine bay. The support flanges 712 are configured to receive jackscrews or other fasteners for attaching the frame 702 to stringers or the hull of the vessel. The jackscrews advantageously transfer torque to the vessels stringers or hull such that the electric motor-generator is prevented from rotating and can apply torque to the propeller shaft. The adjustable jackscrews can allow installation without the need for mounting hardware tailored to a particular engine. Accordingly, additional bracing of the coupling assembly 700 may or may not be required. In some cases, for example, additional bracing may only be needed for vibration damping and does not need to transfer torque. This can simplify the installation and save weight. In some cases support arms 704 are also optionally included for coupling the frame 702 to the ICE drive system (e.g., the ICE or ICE transmission). The support arms 704 can be oriented in any suitable manner in order to effectively attach the coupling assembly 700 to the ICE or surrounding engine bay or other vessel structure.

In the illustrated case, the coupling assembly 700 includes an assembly transmission 720 attached to frame 702. An electric motor-generator plate 722 is attached to frame 702 to attach and support the electric motor-generator 601, and propeller shaft hub support plate 724 is attached to frame 702 to attach and support the propeller shaft hub 706. Typical construction materials for frame 702, support arms 704, support flanges 712, electric motor-generator plate 722, and propeller shaft hub support plate 724 are anodized aluminum and stainless steel (3xx series). The propeller/output shaft can slide through the shaft hub 706 and is secured in some cases with set screws through one or more threaded holes 707. Propeller shaft pulley 726 is configured to be rotatably coupled to the propeller shaft hub 706, and motor pulley 728 is configured to be rotatably coupled to the electric motor-generator 601. Belt 730 rotatably couples the propeller shaft pulley 726 to motor pulley 728 in this case.

FIGS. 9A-9E are side and perspective views, and an exploded assembly view of the shaft hub 706, the assembly bearing 750, the assembly coupling flange 708, and the transmission pulley 726 of the electric motor-generator coupling assembly 700 of FIGS. 8A-8D. The outer race of propeller shaft bearing 750 is configured to attach to, or be supported within, the propeller shaft hub support plate 724 shown in FIGS. 8A-8D. As shown in FIG. 9E, the propeller shaft hub 706 has an interior wall defining an opening 760 that can receive the propeller/output shaft that is operatively coupled to a propeller. In addition, the assembly coupling flange 708 has an interior wall defining an opening 762 that can receive the propeller/output shaft. Accordingly, in some cases the propeller/output shaft can slide through the shaft hub 706 and can be rotationally secured in place with set screws through threaded holes 707 or some other suitable fastening mechanism. Further, in some cases, the propeller/output shaft can slide into the assembly coupling flange 708.

Accordingly, in some cases little or no extra fore and/or aft space is required to install the coupling assembly 700 because the hollow shaft hub 706 and/or flange 708 allow for retrofit installation without the need to move the existing engine forward, which may not be possible in some cases. Referring to FIG. 7A, the fore-aft coaxial length 900 of the propulsion assembly can in some cases be minimal. For example, in some cases the fore-aft coaxial dimension is less than about four inches. In some cases the end of the propeller/output shaft nearest the ICE can be separated from the drive coupling flange of the internal combustion engine by a distance less than the fore-aft length of the propeller shaft hub 706. In some cases the end of the propeller/output shaft nearest the ICE can be separated from the drive coupling flange by a distance less than the fore-aft length of the assembly coupling flange 708. Accordingly, the coupling assembly 700 can be installed about the existing propeller/output shaft with the assembly coupling flange 708 replacing the existing propeller shaft coupling flange, without the need to move the ICE and with the fore-aft dimension of the propulsion assembly taking up minimal space.

Thus, embodiments of the invention are disclosed. Although the present invention has been described in considerable detail with reference to certain disclosed embodiments, the disclosed embodiments are presented for purposes of illustration and not limitation and other embodiments of the invention are possible. One skilled in the art will appreciate that various changes, adaptations, and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. 

1. A propulsion system for a marine vessel, comprising: an internal combustion engine; a first clutch operatively coupled to the internal combustion engine; an electric motor-generator operatively coupled to the first clutch; an output shaft operatively coupled to the internal combustion engine through the first clutch, operatively coupled to the electric motor-generator and configured to be operatively coupled to a propeller shaft; and a controller electrically coupled to the internal combustion engine and the electric motor-generator, the controller configured to adjust a torque load of the electric motor-generator based on a rotational speed of the internal combustion engine and a peak torque output of the internal combustion engine corresponding to the rotational speed.
 2. The propulsion system of claim 1, wherein the controller is further configured to adjust the torque load of the electric motor-generator to load the internal combustion engine with a torque that is within about 30% of the peak torque output corresponding to the rotational speed.
 3. The propulsion system of claim 1, wherein the controller is further configured to adjust the torque load of the electric motor-generator to load the internal combustion engine with a torque that is within about 10% of the peak torque output corresponding to the rotational speed.
 4. The propulsion system of claim 1, wherein the controller is further configured to adjust the torque load of the electric motor-generator to load the internal combustion engine with a torque that is substantially the same as the peak torque output corresponding to the rotational speed.
 5. The propulsion system of claim 1, wherein the controller is further configured to adjust the torque load of the electric motor-generator based on a propeller torque load.
 6. The propulsion system of claim 5, further comprising a propeller shaft operatively coupled to the output shaft and a propeller operatively coupled to the propeller shaft, wherein the propeller torque load corresponds to a torque load of the propeller at the rotational speed.
 7. The propulsion system of claim 6, wherein the propeller is a variable pitch propeller and the controller is further configured to adjust a pitch of the propeller's blades.
 8. The propulsion system of claim 6, further comprising a second clutch operatively coupled between the electric motor-generator and the output shaft for disengaging the output shaft, the propeller shaft, and the propeller from the electric motor-generator and the internal combustion engine.
 9. The propulsion system of claim 8, wherein the controller is further configured to provide at least three operational configurations comprising a first configuration in which the first clutch is engaged and the second clutch is disengaged, to generate electricity with the internal combustion engine and the electric motor-generator, a second configuration in which the first clutch is disengaged and the second clutch is engaged, for driving the propeller with only the electric motor-generator, and a third configuration in which the first clutch is engaged and the second clutch is engaged, for driving the propeller with the internal combustion engine and/or the electric motor-generator.
 10. The propulsion system of claim 1, wherein the controller comprises a computer-readable storage medium storing information characterizing the peak torque output of the internal combustion engine for a plurality of rotational speeds.
 11. The propulsion system of claim 1, wherein the output shaft is rotatable by the internal combustion engine in only a first direction, and the output shaft is rotatable by the electric motor-generator in the first direction and a second direction.
 12. The propulsion system of claim 1, further comprising at least one battery electrically coupled to the electric motor-generator, and wherein the controller is further configured to operate the electric motor-generator with the battery, start the internal combustion engine to charge the battery when the battery reaches a first charge level, and stop the internal combustion engine when the battery reaches a second charge level.
 13. The propulsion system of claim 1, wherein the controller is further configured to start the internal combustion engine when a vessel propelled by the propulsion system is moving faster than a first speed and to stop the internal combustion engine when the vessel is moving slower than the first speed.
 14. The propulsion system of claim 1, wherein the controller is further configured to adjust the torque load of the electric motor-generator by adjusting a value of a charging current of the electric motor-generator.
 15. The propulsion system of claim 1, further comprising a battery and at least one renewable energy source electrically coupled to the controller, wherein the controller is further configured to combine a charging current of the electric motor-generator with a charging current of the at least one renewable energy source to charge the battery, and wherein the controller is further configured to reduce the charging current of the electric motor-generator, as a charge level of the battery increases, before reducing the charging current of the at least one renewable energy source.
 16. A method for propelling a marine vessel, comprising: determining with control circuitry a desired torque output of an internal combustion engine, the internal combustion engine being operatively coupled to an electric motor-generator and a propeller; determining with the control circuitry a current torque output; determining a torque output change by comparing the desired torque output to the current torque output with the control circuitry; and adjusting a torque load of the electric motor-generator with the control circuitry based on the torque output change.
 17. The method of claim 16, wherein the desired torque output is a peak torque output of the internal combustion engine for a rotational speed.
 18. The method of claim 16, wherein determining the current torque output comprises determining a torque load of the propeller.
 19. The method of claim 18, wherein the propeller comprises a plurality of variable pitch blades, and further comprising adjusting the pitch of the plurality of variable pitch blades to adjust the torque load of the propeller.
 20. The method of claim 16, further comprising charging a battery with a charge current produced by the electric motor-generator.
 21. The method of claim 20, further comprising charging the battery with a charge current produced by a renewable energy source and reducing the charging with the electric motor-generator charge current to maximize the charging with the renewable energy source charge current.
 22. The method of claim 16, further comprising monitoring a charge level of a battery coupled to the electric motor-generator, running the internal combustion engine to charge the battery when the battery reaches a first charge level, and stopping the internal combustion engine when the battery reaches a second charge level.
 23. The method of claim 16, further comprising monitoring a speed of the marine vessel, running the internal combustion engine when the marine vessel is moving faster than a first speed, and stopping the internal combustion engine when the marine vessel is moving slower than the first speed.
 24. The method of claim 16, further comprising adjusting the torque load of the electric motor-generator with the control circuitry by adjusting a value of a charging current of the electric motor-generator.
 25. A marine propulsion assembly comprising: a frame comprising one or more supports configured to attach the frame to a marine vessel; a propeller shaft hub rotatably coupled to the frame, the propeller shaft hub comprising an interior wall defining an opening adapted to receive an output shaft operatively coupled to a propeller, the propeller shaft hub further comprising a fastening mechanism to attach the propeller shaft hub to the output shaft in a fixed rotational relationship; a coupling flange attached to the propeller shaft hub, the coupling flange configured to couple to an internal combustion engine; a transmission rotatably coupled to the propeller shaft hub; and an electric motor-generator rotatably coupled to the transmission.
 26. The marine propulsion assembly of claim 25, wherein the transmission comprises two or more pulleys and a belt that rotatably couple the electric motor-generator to the propeller shaft hub.
 27. The marine propulsion assembly of claim 25, wherein the transmission ratio is selected to substantially match the electric motor-generator output speed to a desired speed for the output shaft operatively coupled to the propeller.
 28. The marine propulsion assembly of claim 25, wherein a fore-aft distance required by the coupling flange and the propeller shaft hub is less than about four inches.
 29. The marine propulsion assembly of claim 25, wherein the coupling flange is adapted to replace an existing propeller shaft coupling flange.
 30. A propulsion system for a marine vessel, comprising: the marine propulsion assembly of claim 26; an internal combustion engine comprising a drive coupling flange coupled to the coupling flange of the marine propulsion assembly in a fixed rotational relationship, the coupling flange of the marine propulsion assembly having a fore-aft length parallel to an axis of the output shaft; an output shaft having a first end received within and fixedly attached to the propeller shaft hub, the propeller shaft hub having a fore-aft length parallel to the axis of the output shaft; and a propeller operatively coupled to the output shaft, wherein the first end of the output shaft is separated from the coupling flange of the internal combustion engine by a distance less than the fore-aft length of the propeller shaft hub.
 31. The propulsion system of claim 30, wherein the coupling flange of the marine propulsion assembly comprises a coaxial bore, and wherein the first end of the output shaft is separated from the coupling flange of the internal combustion engine by a distance less than the fore-aft length of the coupling flange of the marine propulsion assembly. 